FR4 PCBA Stencil for SMT Assembly
There are three methods of making SMT stencil:
Apply a layer of anti-acid glue on the steel plate. Remove the glue at the place where the opening is needed, expose the steel plate,it is corroded with acid to form an opening. But the use effect for this kind of steel plate is the worst.
It's very simple to use the laser to punch holes directly where they need to open
This kind of steel plate is made by electroforming the inner wall and the chamfering angle at the opening on the basis of laser engraving, which makes the inner wall of the opening very smooth and convenient to lower the tin.This kind of steel plate is very expensive.
Now more than 95% of the steel mesh in the SMT industry are made by laser cutting.
According to the requirements of various types of stencil openings
CHIP type element is increased by 10~15[%] in the outer three times, keep the inner distance unchanged, and then modified according to the requirement of lead.
The length of IC type elements (including row and plug) shall be added with 0.1-0.20mm, and the width shall be modified to fit the lead.
Discharge, block and capacitance type elements with the length of 0.1mm added. Width can be modified as per lead requirement.
Other components shall remain the same as above.
Acceptance of SMT stencil
Steel mesh tension35≤F≤50（N/cm）, tension error: F is less than or equal to 8(N/cm)
Appearance of SMT stencil: no scratch or bump on the surface.
Before the production of the new stencil, install the stencil correctly on the printing machine, try printing 2-5 times, and confirm the printing effect.
After the trial production is passed, record the production time in the stencil files.
SMT stencil printing format requirement
When one board only one mesh, the position of the open graph should be centered.
When two different PCB boards are opened on the same stencil, the gap between the two boards should be 30mm.
When one stencil open two same PCB, request with 180°in panel and have a 30 mm interval between them.